Asymmetric densitometric and mechanical adaptation of the left fifth metacarpal bone in racing greyhounds

The densitometric and mechanical structural properties of the left and righ t fifth metacarpal bones of 10 racing greyhounds with a fracture of the cen tral tarsal bone and 10 without a fracture were investigated by dual energy x-ray absorptiometry and a servo-hydraulic materials testing machine. In a ll the greyhounds the bone mineral density of the left fifth metacarpal bon e was significantly greater than that of the right (P<0.001), but there was no significant difference between the degree of asymmetry in bone mineral density in the two groups. The ultimate torque and energy-to-failure of the left fifth metacarpal bone of the greyhounds with a fracture of the right central tarsal bone were significantly higher than in the right fifth metac arpal bone and higher than in both the left and right fifth metacarpal bone s of the greyhounds with no fracture (P<0.05). The ultimate torque and ener gy-to-failure were significantly related to bone mineral density (P<0.005), and 22 per cent of the variation in these structural properties could be e xplained by variations in bone mineral density. Fifth metacarpal remodellin g in response to asymmetric cyclic loading is bone-specific, and structural properties are enhanced in the left fifth metacarpal of greyhounds with a fracture of the right central tarsal bone.